For many different kinds of lighting applications, it can be appropriate to use an LED lighting unit that has one or more LEDs arranged at the base of a container or “mixing box”. The light-emitting surfaces of the LEDs face towards a light exit opening of the container, and the side walls of the container or mixing box are generally highly reflective over the entire visible spectrum so that as much light as possible can exit the container through its light exit opening. The LEDs can be mounted on a lead frame or carrier which may even be flexible, allowing many possible shapes and forms for the lighting unit. For example, several tens of red-emitting LEDs can be arranged on a length of flexible carrier and then formed to follow the curved shape at the back of an automobile so that the curved LED lighting unit may be used as a rear lighting unit that follows the styling lines of the vehicle.
The LEDs and carrier of such a lighting unit may be covered by a translucent filler material such as silicone, effectively filling the mixing box to the level of the light exit opening. The filler material may also include scattering particles or tiny air bubbles so that the lighting unit emits a homogenous light in its lit state. A row of individual LEDs with intervening gaps can then take on the appearance of an uninterrupted line of light. The filler material and any scattering particles can also serve to “hide” the light-emitting surfaces of the LEDs in the unlit state.
With the known LED lighting units of the type described above, the high specular reflectivity of the side walls of the mixing box effectively determine the colour of the lighting unit in its unlit state. This means that conventional LED lighting units generally appear as white or silvery-white since the side walls of the mixing box are effectively mirrors that reflect essentially the entire visible light spectrum in their unlit state. This appearance can be perceived as unattractive, particularly for a vehicle with a colour other than white or silver, since the white lighting unit effectively “interrupts” the overall styling of the vehicle. Furthermore, the filler material has a matte appearance, so that that the entire light exit region appears matte, thereby adding to the unwanted noticeability of the lighting unit in its unlit state.
One way of making the lighting unit less noticeable in the unlit state is to include a coloured bezel around the perimeter of the lighting unit, with a colour that matches the vehicle colour. However, this adds to the overall expense, and the coloured bezel cannot entirely hide the white appearance of the lighting unit.
US 2009/0103293 A1 discloses a light emitting diode illumination device with a light emitting diode and a reflective sidewall surrounding the light emitting diode, defining a mixing cavity and partly provided with wavelength converting material.
DE 102 07 585 A1 discloses an illumination device with a light source in a housing. The inner wall of the housing is provided with reflection elements made of coloured paper.
US 2010/0033948 A1 discloses a lighting module comprising a housing with a light source and a reflector in a cavity of the housing.
Therefore, it is an object of the invention to provide an LED lighting unit that overcomes the problems outlined above.